As water pollution generated as a by-product with recent technological advances is becoming worse and worse with improvement in the standard of living, a variety of purification processes for water quality have been developed.
Of these purification processes, a so-called pressure floatation method is employed as a purification process of, especially, closed water regions such as lakes and sea areas. The pressure flotation method is a purification process which comprises the steps of ejecting pressurized water saturated with air dissolved therein from nozzles or slits, allowing fine air bubbles formed by a sharp drop of the pressure to adhere to floating or depositing solids, thereby making the solids rise to form scum, and collecting the formed scum.
Purification techniques using the pressure floatation method are disclosed in, for example, Japanese Unexamined Patent Publication No. 54-75156, Japanese Unexamined Patent Publication No. 5-317847, Japanese Unexamined Patent Publication No. 8112587, and Japanese Unexamined Patent Publication No. 8-132094.
The Japanese Unexamined Patent Publication No. 54-75156 discloses a benthic region purification process. The process includes the steps of dissolving air in water to be saturated under pressures higher than the water pressure of a benthic region to yield pressurized water, ejecting the pressurized water from nozzles placed in the benthic region to form fine air bubbles, mechanically stirring deposits in the benthic region concurrently with the ejecting operation to rise the deposits, allowing the floating matters to adhere to the fine air bubbles, thereby allowing the floating matters to float onto the surface of the water, and collecting and removing scum of the deposits on the water.
The Japanese Unexamined Patent Publication No. 5-317847 discloses a water purifying device which is capable of forming very fine air bubbles by attaching a pressure valve at a tip of a supplying pipe in a region to be treated, and supplying a raw liquid pumped up by the pressurized pump concurrently with supplying compressed gas from a compressor to a vapor/liquid mixing means.
The Japanese Unexamined Patent Publication No. 8-112587 discloses an improvement of the water purifying device disclosed in the Japanese Unexamined Patent Publication No. 5-317847. In the device, both a tip of a pumping tube and a discharge valve at the tip of a discharge tube are placed in a liquid in a region to be treated, and a pump means is operated to supply the original liquid in the region to be treated to a vapor/liquid mixing means. By this configuration, gas supplied through a gas supplying means is mixed with the liquid to be treated to allow the gas to completely dissolve in the liquid.
The Japanese Unexamined Patent Publication No. 8-132094 discloses a fine bubble discharging apparatus. To increase the discharge of a liquid containing dissolved gas and to increase the content of fine air bubbles in the discharge, this apparatus includes a group of injection holes and an outer cylinder outside the injection holes. The outer cylinder has a discharge port which opens either at the end supplying the liquid containing dissolved gas or at the opposite end thereto, and the liquid containing dissolved gas injected from the injection holes is collided with the outer cylinder.
As described above, various improvements in purification apparatuses for use in a pressure floatation method have been made. What is the most important in the pressure floatation method is believed to maximize the volume of fine air bubbles dissolved in a solution. Generally, in the pressure floatation method, the more uniform and smaller particle sizes air bubbles have, the higher the absorbency is and the more quietly the bubbles rise. In addition, such air bubbles do not bubble in an upper layer, and adsorbed flocks and floating matter can be recovered without breaking.
However, to mix gas and a liquid, all of the above apparatuses are provided with a vapor/liquid mixer such as an ejector separate from a pressure pump to supply a vapor/liquid as a mixture of gas and a liquid to the pressure pump. Therefore, the apparatuses as a whole are complicated, and air bubbles to dissolve in the liquid have limited sizes because the gas is mechanically mixed with the liquid. The purification capacity of the apparatuses is thus limited.
Accordingly, an object of the present invention is to provide a vapor/liquid mixer which has a relatively simple structure and is capable of allowing fine air bubbles with a high purification capacity to dissolve in a liquid, and a polluted water purification apparatus using the mixer.